Epihalohydrin electrical stress controlling material

ABSTRACT

A non-tacky electrical stress control material comprising 
     a) about 100 parts of a resin component containing 
     1) from about 20% to about 80% of an epihalohydrin polymer, and 
     2) correspondingly, from about 80% to about 20% of an insulating silicone polymer having a tan δ of less than one, 
     b) from about 10 to about 200 parts of a filler, said filler being nonconductive at room temperature, selected from the group consisting of barium titanate and hydrated aluminum silicate, and 
     c) from 0 to 30 parts of a plasticizer.

This is a division of application Ser. No. 08/694,344 filed Aug. 8,1996, now U.S. Pat. No. 5,804,630 which was a CIP of Ser. No.08/534,390, Sep. 6, 1995 now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to non-tacky conformable material suitablefor use as a void filling, electrical stress controlling material.Specifically, it relates to nontacky core-loadable epihalohydrin polymercompositions which exhibit effective stress control when used at theedge of a semi-conductive shield in a termination either alone or inconjunction with a high dielectric constant tube.

1. Description of the Art

Heat-recoverable rubbery tubular articles and elastically recoverabletubular articles are widely used to cover power cables or conduits. Sucharticles are useful where insulation, sealing and/or encapsulation arerequired. A typical elastically recoverable article is a rubberinsulating sleeve which is provided with an inner support or "core"which holds the article in a deformed shape. The tube is placed over acable, and the core is unwound, and removed. The article then recoverstoward an original shape.

Various compositions have been used in coordination with such articlesto provide electrical stress control and sometimes to bond them tovarious types of pipe and tubing, e.g., mastics, tapes, and greases asin U.S. Pat. Nos. 4,017,652, and 4,383,131.

U.S. Pat. No. 4,363,842 discloses elastomeric pre-stretched tubes formedfrom EP or EPDM with a variety of fillers including carbon black,conductive particles and the like, including carbon black, and aluminumflakes. Barium titanate is disclosed for providing stability ofpermittivity over a wide range of electrical stresses; barium titanatedoes not provide higher permittivity to the elastomeric tubes.

Heat-recoverable articles may also be provided on an inner tube, whichbreaks and allows the elastomeric member to recover. These articles areheated with a hot air gun or torch, to initiate recovery.

Both types of articles may recover around the cable joint or termination(or other substrate) tightly in areas, and have air pockets between thecable and the substrate about which it is recovered in other areas, suchas a semiconducting layer edge, which is highly undesirable. Sealingcompositions, such as greases, adhesives, and the like have been usedwith these articles to reduce or eliminate such air pockets. Many ofsuch compositions have been adhesives which have bonded between therecoverable articles and the substrate about which it is recovered.

EP Patent 0424 090 B 1 discloses an elastomeric covering for connectionsin electrical cables having a conformable material interposed betweenthe prestretched tube and the core, whereby when the core is removed,the elastic forces change the shape and dimensions of the material tocorrespond to the underlying surface. No electrical properties aredisclosed, and a broad range of materials are simply listed.

U.S. Pat. No. 4,378,463 discloses an adhesive for use in heatrecoverable products in areas of electrical stress. The adhesivecomprises an epihalohydrin polymer, a tackifier, a catalyst, and aparticulate filler. The composition bonds the heat-recoverable articleto the substrate, and also provides electrical stress relief. No polymerblends are disclosed.

However, the above composition has some disadvantages. First, it must beprovided separately, and cannot be preloaded into the splice ortermination as the composition will adhere thereto or to the core andeither prevent its removal when it is time to initiate recovery ordeform and fracture during removal, causing the formation of large airpockets.

Applicant has now discovered that a non-tacky stress control materialcontaining an epihalohydrin polymer, and an insulative polymer having atan δ of less than 1, and having certain fillers provides uniqueelectrical properties for use in stress control, i.e., excellentpermittivity. Such compositions exhibit synergism between thecombination of polymers and the fillers not seen when only one type ofpolymer is used with the same fillers. The materials have significantlyimproved results on electrical properties such as permittivity,alternating current voltage withstand tests, impulse withstand, and/ortan δ values.

Further, compositions of the invention may be aged in cable oil andneither swell nor lose their electrical properties.

The compositions may be used alone inside the insulator of an electricalcable, and are suitable for preloading in an elastically shrinkable tubesuch as a splice cover or termination supported on a removable rigidcore, or underneath a pre-stretched elastomeric or heat shrhinkablestress control tube.

SUMMARY OF THE INVENTION

The present invention provides a non-tacky electrical stress controlmaterial comprising

a) about 100 parts of a resin component containing

1) from about 20% to about 80% of an epihalohydrin polymer, and

2) correspondingly, from about 80% to about 20% of a silicone polymerhaving a tan δ of less than one,

b) from about 10 to about 200 parts of a filler, said filler beingnonconductive at room temperature, selected from the group consisting ofbarium titanate and hydrated aluminum silicate, and

c) from 0 to 30 parts of a plasticizer.

Preferred non-tacky electrical stress control materials comprise

a) about 100 parts of a resin component containing

1) from about 20% to about 80% of an epihalohydrin polymer, and

2) correspondingly, from about 80% to about 20% of a silicone polymerhaving a tan δ of less than one,

b) from about 80 to about 120 parts barium titanate, and

c) from 0 to 30 parts of a plasticizer.

The following terms have the defined meanings when used herein.

1. The term "elastically shrinkable" means that an article so describedis in a stretched or radially expanded condition and will shrink toanother condition when permitted to do so, with no heat required.

2. The term "cold-shrinkable" is synonymous with the term "elasticallyshrinkable".

3. The term "core" refers to the supporting article upon which theelastically shrinkable article is deformed in a radially expanded orstretched condition.

4. The terms "insulator" and "insulative polymer" means a polymer with avolume resistivity greater than about 10¹⁰ ohm-cm.

5. The term "epihalohydrin polymer" includes homopolymers, copolymers,terpolymers, etc.

6. The term "tan delta" or "tan δ" refers to the electrical dissipationfactor.

7. The term "permittivity" or "relative permittivity" is the ratio ofelectric flux generated by an electrical field in a medium to thatgenerated by the field in a vacuum.

8. The term "dielectric constant" is synonymous to relativepermittivity.

All ratios, parts, and percents described herein are by weight, unlessotherwise specifically stated.

DETAILED DESCRIPTION OF THE INVENTION

The materials of the invention comprise a resin component which consistsof a blend of two polymeric resins; epihalohydrin polymers andinsulating silicone polymers having a tan δ of less than 1.

Epihalohydrin polymers suitable for use in the compositions of theinvention are the elastomeric polymers of an epihalohydrin inhomopolymer or copolymer form. Such polymers are prepared bypolymerization of the monomeric material in mass or in solution withorganometallic catalysts, and may be homopolymers, copolymers,terpolymers, etc. Examples of homopolymers include epichlorohydrin, orepibromohydrin; useful copolymers include copolymers of epihalohydrinswith alkylene oxides, and copolymers with epoxides, e.g., propyleneoxide, ethylene oxide, butene oxide, and epoxy ethers such asethylglycidyl ether, allylglycidyl ether and the like. Such polymers areavailable from Zeon Chemicals, Inc.

Preferred epihalohydrin polymers include copolymers with alkyleneoxides, particularly ethylene and propylene oxides.

The resin component also contains an insulating silicone polymer havinga tan δ of less than one. Useful silicones include silicones which arefluid at room temperature and gum silicones; gum silicones preferred foreasy compounding and processability; most preferred are those gumsilicones having a durometer of from about 5 to about 30. Surprisingly,silicone polymers having a durometer of 5 or more can be mixed with theepihalohydrin, and provide a product which exhibits faster flow, lowerviscosity and a lower plasticity. The preferred silicones also exhibit aplasticity of less than 250, preferably less than 230.

Commercially available silicone elastomers include those fluid siliconesavailable as Dow Corning DC 10,000, and the like, and gum siliconesavailable as Elastosil® R300/40, and Wacker 7805 and 7815 from WackerSilicones Corporation; Silastic® GP31 from Dow Corning, and the like.

The silicone polymer and the epihalohydrin are present in the resincomponent at a ratio of from about 20:80 to about 80:20, preferably fromabout 30:70 to about 70:30. Formulations comprising less than 20%insulative polymer may be useflul in some applications but exhibit hightan δ values, which is undesirable for high voltage applications.

The composition contains from about 10 to about 200 parts per hundredresin (pph) of at least one particulate filler selected from fillerswhich are nonconductive at room temperature. Preferred fillers arealuminum silicate and barium titanate. Preferred materials comprise fromabout 25 to about 100 parts aluminum silicate or from about 50 to about200 parts barium titanate. The most preferred filler is barium titanate.These resin blends show synergistic behavior with these fillers. Bariumtitanate is available from Ferro Corp. as Transelco 219-3, and hydratedaluminum silicate is available from J.M. Huber as Suprex®.

Materials of the invention exhibit significant improvements inelectrical properties. Barium titanate containing materials exhibitimprovement in permittivity and alternating load current withstandvoltage, i.e., preferred materials exhibit both permittivities of above15 and tan δ of less than 4, preferably around 1. Further, terminationsemploying materials of the invention show improvements in AC withstand;withstanding about 100 kV, terminations employing preferred materialswithstand about 110 kV, as opposed to 95 kV or less for currentconventional electrical stress control materials on 25 kV cable.

Further, there are two failure modes possible in such testing andimpulse withstand testing; external flashover, and internal degradationof the material caused by heat. External flashover is preferred as thetermination or joint is not destroyed and remains functional after thearc exinguishes. Terminations or joints using materials of the inventionhave a failure mode of flashover as opposed to those using conventionalsealants which have a degradation failure mode.

Finally, materials of the invention show stability and integrity evenwhen aged in oil for extended periods of time at high temperatures.Terminations or joints formed from the materials of the invention willexhibit identical electrical properties, or even improved properties andstructural integrity even after being immersed in polybutene oil (thetype used in paper insulated lead cables) for 90 days at 90° C.Conventional materials, such as those containing EP or EPDM type rubberswill swell after such aging and lose the electrical properties, such asdielectric constant.

Hydrated aluminum silicate containing materials exhibit superior tan δvalues while retaining useful permittivities.

Materials of the invention may also comprise a plasticizer. Usefulplasticizers include aliphatic, naphthenic, and aromatic petroleum basedhydrocarbon oils; cyclic olefins (such as polycyclopentadiene);polyalphaolefins (such as hydrogenated polymerized decene-1),hydrogenated terphenyls or other terpene derivatives; polypropyleneoxide mono- and di-esters, cyclopentadiene copolymers with fatty acidesters; phosphate esters and mono-, di-, and poly-esters, (such astrimellitates, phthalates, benzoates, fatty acid ester derivatives,fatty acid ester alcohols, dimer acid esters, glutarates, adipates,sebacates, polymeric polyesters, rosin esters, acrylate esters,epoxidized fatty acid esters, and the like) and mixtures thereof

Preferred plasticizers include phosphate esters and polyesters andpolyethers such as adipates, phthalates, azelates, and the like, i.e.,dioctylphthalate, and dioctylazelate. The latter is available from C.P.Hall, as Plasthall® DOZ. The plasticizer may be present in an amount upto about 30 parts per hundred parts of resin.

The stress control materials may also include up to about 15 parts (pphresin) of metal flake or other conductive filler such as aluminum flake,or copper flake. Aluminum flake, such as that available from SilberlineMfg. Company as Silvex® 620-25-A, is preferred.

Materials of the invention may also contain minor amounts of otheradjuvants such as antioxidants, dyes, pigments, flame retardants,release aids and the like so long as the addition does not negativelyaffect the electrical properties. Useful antioxidants include Agerite®MA, available from R. H. Vanderbilt Co. Useful process aids includefatty acids such as ATMER™ 103, available from ICI Americas, andKemamide® U, available from Humko Chemicals.

Materials of the invention are especially useful in medium or highvoltage power cables. The composition of the invention may be usedalone, e.g., placed under an insulator of such cable in the region ofthe semiconductive cutback to fill voids. However, many cable joints orterminations use a pre-stretched stress control tube as well. Typically,pre-stretched tubes are provided on a rigid easily removable core. Thecore can be external or internal; however internal cores are preferable.Typical cores are such as those described in U.S. Pat. No. 3,515,798,incorporated herein by reference. Preferred terminations comprise acoordinated two-component or three-component stress-control system wherethe inner component is the conformable material of the invention, andthe outer component is the high permittivity tubing. Alternatively, twolayer structures include the material of the invention and an outerlayer which is an insulator having high permittivity. A possible thirdlayer is a polymeric insulator, typically a pre-stretched tube such asthose described in U.S. Pat. No. 4,363,842, incorporated herein byreference.

When materials of the invention are used in such terminations, theelectrical stress control is greatly improved, which allows asignificant reduction in the required length of the termination. i.e.,at least about 20% reduction, which reduces costs and installation spacerequirements. Preferred materials may allow a length reduction of 40% ormore. The application of silicone grease is no longer required, nor isthe application of tape or other sealing materials at the ends of thetermination, as it may be sealed with the stress control material, whichis core loadable, permitting its automatic delivery. Materials of theinvention are typically loaded at thickness of from about 1.25 mm toabout 3 mm, preferably from about 2 to about 3 mm.

Compositions of the invention are prepared by mixing the ingredients andthen pressed, extruded, injection molded or calendared into the finalform desired. The final product can be provided as sheets, shapedarticles, or in putty form, as desired for the application.

The following examples are for illustrative purposes only, and are notmeant to be limiting. One skilled in the art will easily think ofvariations within the scope of the invention, which is solely thatdefined by the claims.

TEST METHODS Alternating Current Withstand and Basic Impulse WithstandVoltage Tests

The International Society of Electrical and Electronic Engineers (IEEE)sets the United States standard for high voltage cable; the test isconducted per IEEE48. In order to determine the limit of AC withstand,AC withstand voltage is increased in steps of 5 kV per hour untilflashover or internal degradation breakdown occurs. In order todetermine the limit of impulse withstand, impulse voltage is raised insteps until flashover or internal degradation breakdown occurs.

Electrical Properties

Electrical properties (permittivity, tan δ) were tested according toASTM-D 150 using an impedance measurement method. The electricalproperties were tested at an electrical stress of about 3 kV/cm to about20 kV/cm.

Probe Tack Test

The probe test was performed according to ASTM D-2979.

Rubber Property-Plasticity and Recovery (Parallel Plate Method)

This test was performed according to ASTM D926-93, procedure A.

Adhesion to Core

For this test, a stress control material was placed onto a rigid corefor an elastically shrinkable splice or termination by means of fingerpressure. The core was then unwound, and the material was observed fordeformation, fracture and adhesion to the core.

For samples which survived such test without deformation or fracture,another identical sample was placed on the core and an elasticallyshrinkable splice cover was placed onto the core. The sample was storedfor 3 months, and then the core was unwound, and the material checkedfor deformation, fracture and adhesion to the core.

EXAMPLES Example 1

Preparation of the Material

86.87 g of Hydrin® C45, 115.15 g of Dow-Corning Silastic® GP3 siliconeelastomer, 20.20 gms of dioctyl azelate, available as Plasthall DOZ®,72.73 gm of Transelco 219-3 barium titanate, 2 gm Kemamide® U, and 3 gmof Silcogum® black 095 black pigment were placed in the order listed,with the barium titanate being added in two steps in an internalBanbury® mixer at 60-80 rpm and each ingredient permitted to mix beforeadding the next. After all ingredients were added, the ingredients weremixed until the batch temperature reached at least 70° C. The batch wasthen dropped from the mixer and placed in sheet form onto a two rollmill, adding any material remaining in the pan.

Other materials were prepared on a two roll mill by setting the rolltemperature to 60° C., adding the epichlorohydrin, and allowing it toband both rolls, and then mix for about two minutes. The silicone wasthen added, and mixed until the color was even. The barium titanate andplasticizer were added together, and mixed until dispersed. The pigmentwas added and mixed. The batch was then removed and allowed to cool.

Preparation of Test Samples

Samples of from about 1 mm to about 3 mm in thickness were prepared bypressing between parallel metal plates in a hydraulic or pneumaticpress, using shims to set the final plate separation.

First, the material was made as described above, and then a sample wascut, placed between the plates and pressed for about 5 minutes. Thesample was then inspected carefully to ensure no foreign matter orentrapped air was visible, as clean samples are required to insureproper dielectric testing.

Examples 2-4 and Comparative Examples C5-C8

These formulations of the invention were compounded as described inExample 1, except with differing ratios of resins and differing fillers.Suprex® clay is hydrated aluminum silicate, available from J.M. HuberCo. Example 4 contains no plasticizer.

During processing of various batches of material for Example C6, thebatches became "nervy", i.e., it lost its smooth flowability and waslumpy, and difficult to further process into slabs or sheets. Clearly,processing time is critical, and good primary and secondary processingis very difficult to acheive with this material.

                  TABLE 1    ______________________________________    Ingredient/Example    No. (pph*)  1     2     3   4     C5  C6   C7   8    ______________________________________    Hydrin ®                50    50    50  50    84  50   --    30    Silastic ® GP31                50    50    50  50    16  50   60   --    Wacker R300/30                --    --    --  --    --  --   --    70    Nordel 1440 --    --    --  --    --  --   40   --    Hectorite Clay                --    --    --  --     4  20   --   --    Plasthall DOZ ®                10    10    10  --     5  --   --   --    Suprex ® Clay                --    --    29  --    --  --   --   --    BaTiO.sub.2 60    60    --  60    --  --   60   100    Aluminum Flake                 8    --    --  8.5   --  --   8.5  --    Kemamide ® U                 2     2     2  2      2   2   2     3    SilicoBlack 95                 3     3     3  3      3   3   3     3    ______________________________________     *parts per hundred resin

The formulations described in Table 1 were then made into samples andelectrical properties were tested. Results of those tests are shown inTable 2.

Example 4 was also tested in a termination having a tubular design, witha 21.6 cm insulation shield cutback, an overall length of approximatly33 cm. The electrical stress control material was placed into thetermination at a thickness of 2 mm. The termination was tested on a 25kV 1/0 AWG cable, Jacketed Concentric Neutral. The AC Withstand was 120kV with the failure mode being flashover, and the Maximum ImpulseWithstand was +195 kV, and +196 kV, for Positive and Negativepolarities, respectively.

Example C7 is an embodiment of U.S. Pat. No. 4,363,842 (Nelson). As isshown in Table 2 below, a material using a silicone/EPDM constructionrather than the silicone epihalohydrin blend resins of the invention.Such material does not have a good dielectric constant even when 8.5parts of aluminum flake is added, only reaching 4.47.

It is desirable to have a combination of a dielectric constant above 9,preferably above 10, and a tan δ of less than 4. Note that for thecomparative examples C5 and C7, this combination is not met, while eachof the examples of the invention meets these criteria. C5 becomesresistive, e.g., at high stresses, which is extremely undesirable.Comparative example C6 shows reasonable electrical properties; however,as noted above, processing of this material is very difficult.

                  TABLE 2    ______________________________________    Elec    Properties/Example No.                 1      2      3    4    C5  C6   C7    ______________________________________    tan δ *                 2.9    2.8    0.77 2.9  58  3.3  .022    dielectric constant*                 49     36     11   49.2 28  17.7 4.47    ______________________________________     *These numbers are the average dielectric constant and dissipation factor     tan δ, over electrical stresses from 3,000-20,000 v/cm.

Example 8

A sample was made according to the invention containing the followingingredients; 30 parts Hydrin® C-45, and 70 parts Wacker R300/30silicone, 100 pph Transelco BaTiO₂, 3 pph Kemamide® U, and 3 pphSilicogum Black 0.095. The composition was tested for electricalproperties as discussed above, and found to have an average dielectricconstant of 35, and an average tan δ of 0.97. The sample had an averageplasticity according to ASTM D926-93 of 235.

The sample was then aged in cable oil, i.e., polybutene oil for 90 daysand 90° C. The dielectric constant rose an average of about 2% aftersuch aging.

Example C9

An example of the mastic disclosed in U.S. Pat. No. 4,378,463 wasprepared as described. This sample along with samples 1, 2 and 3 of theinvention were subjected to the probe tack test. Example C9 had anadhesion to the core such that upon unwinding the core, the adhesivedeformed and fractured along the separating helical core weld lines, andremained firmly adhered to the unwound core strand.

The Examples of the invention all allowed unwind without any visibledeformation or fracture, and did not adhere to the core. Further samplesof Examples 1-3 were then placed upon cores, and elastically shrinkablematerial of U.S. Pat. No. 4,363,842 was placed thereover. These werestored at ambient temperatures for 60 and 90 days, and then removed. Theelectrical stress control material even after such storage associatedwith the elastomerically shrinkable material and did not adhere to thecore, nor were any deformations or fractures visible.

A room temperature probe tack was also run on Example C9, and Examples1-3. The results were as shown in Table 3.

                  TABLE 3    ______________________________________                         Probe         Temp   Dwell    Speed Sample Max.    Ex.  (° C.)                Time (s) (cm/s)                               Holder Force (g)                                             Comments    ______________________________________    C9   23     100      0.01  aluminum                                      101    did not                                             debond    C9*  23     20       0.01  aluminum                                      283    did not                                             debond    1    23     100      0.01  aluminum                                      Not    no adhesion                                      Applicable    ______________________________________     *Steel backing used to limit deformation of material.

A sample was made according to the invention containing the followingingredients: 30 parts Hydrin® C-45, and 70 parts Wacker 7805 silicone,100 pph Transelco BaTiO₂, 3 pph Kemamide® U, and 3 pph Silicogum Black0.095. The composition was tested for electrical properties as discussedabove, and found to have an average dielectric constant of 28.34 and anaverage tan δ of 0.85. The sample had an average plasticity according toASTM D926-93 of 208.

What is claimed is:
 1. A non-tacky electrical stress control materialcomprisinga) about 100 parts of a resin component consisting of a blendof1) from about 20% to about 80% of an epihalohydrin polymer, and 2)correspondingly, from about 80% to about 20% of an insulating siliconepolymer having a tan δ of less than one, such silicone being a gumsilicone having a durometer of from about 5 to about 30, b) from about10 to about 100 parts hydrated aluminum silicate, and c) from 0 to 30parts of a plasticizer,said material having a permittivity greater thanabout 15, and a tan δ of less than 4 when tested under electrical stressof from at least about 3 kV/cm to about 20 kV/cm.
 2. A non-tackyelectrical stress control material according to claim 1 wherein saidmaterial has a tan δ of less than 1 where said material is tested underelectrical stress of from about 3 kV to about 20 kV/cm.
 3. A non-tackyelectrical stress control material according to claim 1 wherein saidresin component consists of from about 30% to about 70% of anepihalohydrin polymer, and correspondingly, from about 70% to about 30%of a silicone polymer having a tan δ of less than one.
 4. A non-tackyelectrical stress control material according to claim 3 furthercomprising from about 1 part to about 15 parts per hundred parts of theresin component, of a metal flake.
 5. A non-tacky electrical stresscontrol material according to claim 4 wherein said metal flake isaluminum flake.